Analytical sensor systems that can monitor interactions between molecules, such as biomolecules, in real time are gaining increasing interest. These systems are often based on optical biosensors and usually referred to as interaction analysis sensors or biospecific interaction analysis sensors. A representative such biosensor system is the BIACORE® instrumentation sold by GE Healthcare, which uses surface plasmon resonance (SPR) for detecting interactions between molecules in a sample and molecular structures immobilized on a sensing surface. As sample is passed over the sensor surface, the progress of binding directly reflects the rate at which the interaction occurs. Injection of sample is followed by a buffer flow during which the detector response reflects the rate of dissociation of the complex on the surface. A typical output from the BIACORE® system is a graph or curve describing the progress of the molecular interaction with time, including an association phase part and a dissociation phase part. This binding curve, which is usually displayed on a computer screen, is often referred to as a “sensorgram”.
With the BIACORE® system (and analogous sensor systems) it is thus possible to determine in real time without the use of labeling, and often without purification of the substances involved, not only the presence and concentration of a particular molecule (analyte) in a sample, but also additional interaction parameters, including kinetic rate constants for binding (association) and dissociation in the molecular interaction as well as the affinity for the surface interaction. The association rate constant (ka) and the dissociation rate constant (kd) can be obtained by fitting the resulting kinetic data for a number of different sample analyte concentrations to mathematical descriptions of interaction models in the form of differential equations. The affinity (expressed as the affinity constant KA or the dissociation constant KD) can be calculated from the association and dissociation rate constants. It is also possible to measure affinity values by equilibrium binding analysis, which involves determining, for a series of analyte concentrations, the level of binding at equilibrium, or steady state, which is presumed to have been reached at or near the end of the association phase of the binding interaction.
In the current approach, the methodology strives to obtain highly repeatable, high quality response signals. This is achieved by several time-consuming measures like long injection or contact times (greater than 30 seconds) to have high and stable response values; washing the fluidics system to avoid disturbances; carry-over control injections to monitor response contribution from pollutions of the fluidics; and regeneration to bring the sensor surface to the same start condition in every cycle. These steps can be very time consuming, and resulting cycle times can typically reach 600 seconds or more. Such long cycle times can lead to significant runtimes, particularly so where there is a need to assess multiple analyte samples in a single experiment.
The present invention at least partially aims to overcome the problems associated with current methods of assessing interactions between an analyte and a ligand using a biosensor.